Turbo charged engines may utilize a Charge Air Cooler (CAC) to cool compressed air from the turbocharger before the compressed air enters the engine. Condensate may form in the CAC depending on the amount of cooling and humidity of the intake air, especially during humid or rainy weather conditions, as the intake air is cooled below the water dew point. When the intake air includes recirculated exhaust gasses, the condensate can become acidic and corrode the CAC housing. The corrosion can lead to leaks between the air charge, the atmosphere, and possibly the coolant in the case of water-to-air coolers. Condensate may accumulate in the CAC, and then be drawn into the engine at once during times of increased air mass flow, increasing the chance of engine misfire.
Other attempts to address condensate formation include restricting intake air travelling through the CAC or restricting cooling ambient air flow to the CAC. One example approach is shown by Craig et al. in U.S. Pat. No. 6,408,831. Therein, the intake air temperature is controlled by an ambient air flow restriction system and an intake air flow restriction system. A controller defines the position of these restriction devices in response to ambient temperatures and atmospheric temperature and humidity.
However, the inventors herein have recognized potential issues with such systems. Specifically, the above control systems in response to ambient air temperature and humidity may reduce condensate in some situations; however, these variables may not accurately track the level of condensate in the CAC. Additionally, not all vehicles may be equipped with humidity sensors. Thus, control systems as described above may be adjusted using other variables which may not accurately estimate condensate formation of the CAC. Therefore, condensate formation and engine misfire may not be adequately reduced.
In one example, the issues described above may be addressed by a method for adjusting an operating parameter, such as grille shutters or CAC purging operations, in response to condensate formation in a CAC. The condensate formation may be based on ambient humidity and the humidity may be based on CAC efficiency. In this way, a more accurate CAC condensate level may be determined and used to control other engine systems to reduce condensate formation and engine misfire.
As one example, in response to a CAC condensate level, engine operating parameters may be adjusted. Adjusting engine operating parameters may include adjusting a grille shutter system, an electric fan, and airflow through the CAC. Airflow through the CAC may be adjusted by increasing the opening of an intake throttle, adjusting a valve of a variable volume CAC, and/or downshifting a transmission gear. The amount of condensate in the CAC may also be used to initiate CAC condensate purging operations and control transmission gear downshifting operations to reduce engine misfire. The CAC condensate level may be based on ambient humidity which may be determined from CAC efficiency. In one example, when CAC efficiency is greater than a threshold, a higher humidity value may be set, inferring the presence of rain. In another example, when CAC efficiency is less than a threshold, a lower humidity value may be set. The higher humidity value may be substantially 100%, while the lower humidity value may be less than the higher humidity value. CAC efficiency may be based on CAC inlet and outlet temperature, such when the vehicle speed is greater than a threshold to provide sufficient flow across the CAC. Additionally, the humidity value may be estimated to the higher humidity value when windshield wiper speed is above a threshold speed.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.